Multiconductor system for signaling circuits



Oct. 3, 1933. H. NYQUIST 1,928,735

MULTICONDUCTOR SYSTEM FOR SIGNALING CIRCUITS Filed March 19, 1952APfipatem I .JVEar-End Crasstallc Far-End O-osstalk BB/agate lull, 7 wPair 2 xx Reflection, Point .Eeflected JVd r-Z'nd O'asstalk Z lie/wadedWa'we Reflection, Point Pan 7 K g R\ Pair-2 War End Crostabl: .Tar 17ndCrosstalk Zine Far End Crosstabl:

fZzr-Zrzd Crosstalk (Jonah/med zmltlp Ma /End Ovsszzzlk with PgflectwmsFu lhd Cross talk Fre qaenc INVENTOR BY W ATTORNEY Patented Oct. 3,-1933;

MULrmoNnUc'r'oa srs'mrr I srcnmnc omcmrs .pnmINyqms-t 'Miuburn N.J.,'assi "1i Ame ica Telephone and Telegr p Company;

f comratio 'of New W I v Application March 19, 19.32; ,599,998: 'T

' em m. (01. 9-78) i i Y A principal object or my invention is toprovide a new and improved system for neutralizing crosstalk inmulti-co'nductor cables. In this connection it is a further object toprovide a mutual in- 1 the self-inductance ina single pair incidental tosuch a cross connection. Still another object of self-inductance'bymeans of capacities properly connectedffiAll these objects and variousother objects and advantages of my invention w n become apparent onconsideration of;aspeciflc 'example of practice according-totheinvention. It

will be understood that the following description relates principally tothis particular example of} the invention and that its scope will beindicated inthe appended claims; r

In the accompanying drawing; Figure a 'diagrarn'atic representationoisever'al conductor pairs and a crosstalk balancing panel therefor;

. Figs. 2 and3' are diagrams to=illustrate atypical used inexplainingthe effect of reflections in the circuit"upon'fthe "crosstalk;and Fig. 4 is'a curve diagram that will be used in this connection.

In Fig. 1 four conductor. pairs 1, 2, 3 and 4 are represented as passingacross the panel board 5. In this diagrammatic representation it isassumed that there are crosstalk effects between each pair and each ofthe other pairs, and that these efiects are neutralized by mutualinductance connecr tions between one side of each pair and a side ofeach other pair. connections are all'represented as adjustable, one suchconnection being indicated, for example, at 6 between one side of pair 1and.one side of pair 2. s V s The mutual'inductance linkage between thetwo coils as at 6 will involve a considerable amount of self-inductancein each conductor corresponding to a coil. That is, due-to the mutual inductance 6 there will be a certain amount oi selfinductance in each ofthe circuits 1 and 2. Even if the coils at 6 were wound with the utmostcare to reduce self-inductance there would necessarily be someself-inductance if there is to be mutual.

inductance between the two windings. In practice, the adjustment of themutual inductance amount of self-inductance in each circuit.

due to the mu ual du ance 6 m y be, there ductance cross connection froma conductor of-one; pair'to a conductor of another pair, and in com-,bination therewith to providemeans to neutralize;

} Further, in Fig, 3, apartof themain transmission-wave isshownrefiectedbackat the reflection group of crosstalk paths;these'idia'gramswillbe} 7 pair 2. New therelative phases between theseThese mutual inductance A a in efiecting a neutralization of thecrosstalk. may be by moving the coils to or from each other 7 and inthat case there may be a very considerable M Whatever theself-inductance in circuits 1 and j 2 will: be additionalself-inductanceineach circuit .due to; the mutual inductance connectionswith other circuits such as 3, and 4. .The'drawingis diagrammatic and inpractice there may be one hundred ;pircuitsqmore or less,- 1 and any oneof 3 these circuits may ,have mutual inductance connections with alargenumberof the other circuits 1 so -that the total, self-inductancein each-circuit v rnay become of considerable magnitude; 0' myinvention-'{is to'effect such neutralization of schematically inFigs. 2and 3 for twopairs, pair 1 which is the energized pairand pair 2 whichis the disturbed pair.- In Fig.2 the near-end crosstalk wave which flowsback toward the reflection point in pair 2;is here reflectedand combineswith the direct or v true far-end crosstalk that pair."

point in pair 1. This reflected wave gives nearfend crosstalkwhichffurtheraddsto, the reflected near end ,crosstalkand the far-endcrosstalk in three crosstalk waves in pair 2 will vary with thefrequency at which pair 1 is energized. A plot illustrating a possiblevariation of far-end crosstalk with this frequency is shown in Fig. 4.The direct or true far-end crosstalk is substantially directlyproportional" to the frequency. Whenthe near-end crosstalk combined withthe reflections is'added to the true far-end crosstalk, at somefrequencies in phase addition, at others in. phase opposition, theresultant far-end crosstalk frequency characteristic becomes a sinuousor such neutralization becomes much more difiicu1t-- 'or'impossible whenthe crosstalk varies in a more or less irregular manner such, iorexample, as illustrated by the curve showing the resultant crosstalk.Thus the existence of such reflection points in the circuits causes adefinite hardship To remedy this condition, condensers of proper Thesecondensers are represented in the.-

where l L is {the total self-inductance jinjthe corresponding circuitdue to the mutual inductance connections between that circuit and other'circuits, and K is the'nominal characteristicjm pedance of theconductor pair (that is K= /L'/c', where L is the self-inductanoemf thPair tance of the pair per unit length). At'highifre quencies K will bevery nearly canal .to .the re sistance' component of theactualimpedance.

With the capacities introduced as ghown, and with the values stated, theimpedance will be- [come the same *looking both ways as- 'at "such a";point as Agand the objectionable'refiection'eflects that have benmentioned will be obviated. I olaimz V a 1.-"In -"oombination, '-aplurality -ot neighboring oonduotor pairs--tor signalingmach being'eabto--cross-talk -irom other m, -a. *-rr rutua1' inductance conneotlon'between a conductor of one pair an'd a'-c0nduotor or another pair, ;said'induotancebeing'adjusted toheutralize the crosstalk, and a' between theconductors of one such pair to compensate the self inductancecrouch-mutual induotanoeconnections;

2. In'combination, a plurality of neighboring conductor pairsfor-signaling, mutual inductance connections between some of theconductors of -diflemntpaira and oondensers connected'between theconductors of the-respective pairs, these-condensers being given thecapacity values to neutralize the lumped impedance to make the oyerallcharacteristic impedance sameboth ways along the conductor pairs;combination, a plurality of neighboring conductor pairs forsignalingpaplurality of -mu- -:tual induotanoes each oonnecteelbetween aconductor of one pair and a conductor of another pair to reducecrosstalk between such pairs, and condensers, there being two of thesecondensers respective to each pair involved in the aforesaid mutualinductance connections, each of such two condensers being of thersamecapacity value and at a respective side of;allthe,mutual inductanceconnections involving the respective pair, the total capacity C of suchtwo condensers satisfying the equation the total self-inductance of thecorper unit length of circuit, andflfflszthe mutuaLcapaoi-;

Jmfiedance DI that pair.

4. The method of neutralizing crosstalk between-neighborin'giconductorpairs which consists inestablishing mutual inductance effects betweenthem and obviating the reflection due to the t-lurnped impedance :natureof :the incidental self dnductanoerineachgpair bymaking cross-capacity-conne,ctions;hetween the:sides of :each pain i zlnicombination, aplurality :of neighboring rconductorpairs witha v normalitendency213011055 .talkhetweeneachsuch pa'ir and eachnof, the other-pairs,--adjustable;mutua1 inductances between the E-same ,pairs whereby;,a certain inevitable amount of self induction :is introduced in:each'such -pair, veach sfli 'zmutual inductance being adjusted to'zannul the ztendency to 'crosstalk, and adjustablezcondensers,acrosseach .said;pair, said condensers @beingradjustedinrelation -to;said:self inductances to give a smooth characteristicimpedance along yeachpair andobviate reflection efiects. ,iB. The method0f neutralizing rcrosstalk Ebetween neighboring conductor pairs withoutin- ,troducing 1reflection-efiectsyivhich consists in establishingmutual inductance effects rbetween sa'id pairs directly toneutralizecrosstalk, and introducing .;oapacity ieffects ;across each pair ;to,neutralize "the self inductance :in such pair incidental to the mutualinductance between such mihandrother pairs.

.[HARRY NYQUIST.

